Amazon Handmade UK – refund initiated (Unable To Deliver)

Hello,

I’m a new FBM handmade seller and just received notification of a refund initiated with the reason: Unable To Deliver.

This was a custom order and sent with Royal Mail tracked services. I’ve checked the tracking and it doesn’t appear to have moved in 10 days or so.

I’ve had no contact from the customer and was only made aware of the delivery issue when Amazon just sent through the refund.

Any advice on how to handle this situation as a new seller?